1. Field of Invention
This invention relates to electrical geophysical methods and apparatus for determining the in-situ density of homogeneous porous materials.
2. Description of Related Art
In-situ density calculations using electrical geophysics were developed by Anderson and Ehni in 1996, using resistivity measurements and porosity calculations as developed by G. E. Archie, combined with a formation factor or constant. These formation and/or solution factors are empirically derived through experimentation and testing for repeatability.
The invention involves a process and apparatus requiring specific measurements using equipment consisting of a resistivity meter and a series of electrodes (in groups of four) set up in an array which directly measures the electrical resistivity of a homogenous porous medium, such as compacted fill for the roadbase of a highway or foundations for building construction. The testing process is non-destructive, fast, and can be conducted during and/or after the material has been installed. Electrical resistivity data are collected in the field and are used to calculate the in-situ density of the construction site at the time of field investigation. The test methodology includes a set of standard operational techniques for acquiring the electrical resistivity data which is used to quantify the porosity of the earthen material and qualitatively calculate the in-situ density the earthen material.
Development of an electrical geophysical method and apparatus for determining the in-situ density of porous materials at the earths surface utilizes two primary principles of applied geophysics. Both of the geophysical principals had their origin in the petroleum industry and were not considered, assessed, examined, or adapted for use for geotechnical engineering until Anderson and Ehni recognized their potential, conducted research to assess adaption of the principals, and developed the invention that is presented herein.
The first geophysical principal is based on work by Conrad and Marcel Schlumberger (1930) who developed a system of measuring the resistivity of surface rocks with electrodes deployed on the surface. They used the subsurface zone variations in resistivity to interpret gross geologic structural phenomena. They later applied this technology to evaluating the lithology of well bores that were drilled for petroleum exploration.
The second geophysical principal uses G. E. Archie's 1941 work. Archie presented his work in 1942 in a paper entitled The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics. Archie determined porosities of various materials using resistivity measurements. Mathematical formulas that G. E. Archie derived, and other relevant mathematical formulas that have been adapted for use in the invention.
By adapting these two petroleum exploration and production industries principles for use with modified geotechnical engineering equations for earthen material density, a new, accurate method has been developed for determining the in-situ density of porous materials at the near surface.
The following prior art reflects the state of art of which the applicant is aware and is included herewith to discharge applicant's duty to disclose relevant prior art. However, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
Anderson, D. M. and Ehni, W. J., Geophysical Methods and Apparatus for Determining the Hydraulic Conductivity of Porous Materials, U.S. patent application Ser. No. 08/370,102 filed on Jan. 9, 1995. Continuation In Part, filed Apr. 15, 1997 by Patent Agent, Ian Burns, Esq., Attorney Docket No. :1273.01 PA1 Archie, G. E., The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics, Transaction of the American Institute of Mining and Metallurgical Engineers, Vol. 146, 1942 PA1 American Society for Testing and Materials (ASTM), ASTM D 1557-78 or 698-78 Standard Test Methods for Moisture-Density Relations of Soil and Soil Aggregate Mixtures, 1988 Annual Book of ASTM Standards, 4 Construction, Philadelphia, Pa., 1988 PA1 Bowles, J. E., Engineering Properties of Soils and Their Properties, McGraw-Hill, New York, 1992 PA1 Cernica, John N., Geotechnical Engineering: Soil Mechanics, Wiley, N.Y., 1995 PA1 Hunt, Roy E., Geotechnical Engineering Investigation Manual, McGraw-Hill Book Company, New York, 1984 PA1 Parasnis, D. S., Principles of Applied Geophysics, Fourth Edition, Chapman & Hall, New York, N.Y., 1986 PA1 Schlumberger C., and Schlumberger M.; Depth of investigation attainable by potential methods of electrical exploration . . . ; AIME Technical Publication No. 315; 1930 PA1 Schlumberger C., Schlumberger M., Leonardon E. D.; Electrical Coriing: a Method of Determining Bottom-hole data by Electrical Measurements.; Transactions of the AIME; Technical Publication No. 462; 1932 PA1 Wyllie, M. R. J. and Rose, Walter D., Some theoretical Considerations Related to the Quantitative Evaluation of the Physical characteristics of Reservoir Rock from Electrical Log Data, Gulf Research and Development Co., AIME Petroleum Branch, 1949 PA1 "After the materials have been satisfactory mixed, the mixture shall be bladed and compacted to a ninety-five (95) percent relative maximum density as determined by Test Method No. Nev. T101. Test Method No. Nev. T102 or T103 may be used to determine the in-place density. Test method to be determined by the Engineer."
Related patent applications
U.S. patent application Ser. No. 08/370,102 with filing date Jan. 9, 1995, and Continuation In Part, filed Apr. 15, 1997 by Patent Agent, Ian F. Burns, Esq., Attorney Docket No. :1273.01; and Patent Cooperation Treaty Application No. PCT/US96/00355 with international filing date 11 JAN 96 are related to this patent application. The title of the above mentioned applications is: Geophysical Methods and Apparatus for Determining the Hydraulic Conductivity of Porous Materials. D. M. Anderson and W. J. Ehni are co-inventors and co-applicants for the above mentioned patent applications. The apparatus and method of acquiring the electrical resistivity field data for determining relative in-situ density of porous material uses portions of the prior art. However, in the invention disclosed herein the data digest and integration of different mathematical equations and expressions produces a relative density result from the measured resistivity data.
Provisional Patent Application with Ser. No. 60/017,660 filed with the US Patent and Trademarks Office on May 14, 1996, titled Electrical Geophysical Methods and Apparatus for Determining the Percent (%) Moisture of Porous Materials was filed by D. M. Anderson and W. J. Ehni.